Since that time, I have found no earlier thinker who has described forced religion as the rape of the soul, but I have found what may well be the first description of it as a "molestation." The rescript of Licinius, published in 313 A.D., documents the Edict of Milan formulated by Constantine and Licinius. Though they failed to abide by this edict, it is a remarkably enlightened statement and may well be the earliest legal document affirming religious liberty.
Here is an English translation of the Edict of Milan:
When we, Constantine Augustus and Licinius Augustus, had happily met together at Milan and considered all things which pertain to the advantage and security of the state, we thought that, among other things which seemed likely to profit men generally, we ought, in the first place, to set in order the conditions of the reverence paid to divinity by giving to Christians and all others full permission to follow whatever worship any man has chosen. Thereby whatever deity there is in heaven may be benevolent and propitious to us and to all placed under our authority. Therefore we ought, with sound counsel and right reason, to lay down this law, that we should in no way refuse to any man any legal right who has given up his mind either to the observance of Christianity or to that worship which he personally feels best suited to himself -- to the end that the Supreme Divinity, whose worship we freely follow, may continue in all things to grant us his accustomed favor and good will. Wherefore your excellency [addressed to the governors of the provinces] should know that it is our pleasure that all provisions whatsoever which have appeared in documents hitherto directed to your office regarding Christians and which appeared utterly improper and opposed to our clemency should be abolished, and that all who wish to worship as Christians may now freely and unconditionally do so without any annoyance or molestation. These things we thought it well to signify in the fullest manner to your attention, that you might know it well to signify in the fullest manner to your attention, that you might know that we have given free and absolute permission to the said Christians to practice their worship. And when you see that we have granted this to the said Christians, your excellency will understand that to others also a full and free permission for their own worship and observance is granted, for the tranquillity of the times, so that every man may have freedom in practice of whatever worship he has chosen. (Emphasis mine)